2019 – WEEK 4, ROBOT ASSEMBLY
This week we started getting the parts in to assemble the robot. Custom parts were being milled, turned, welded and laser cut. Prefab parts had been ordered and were eagerly awaited. The very first system we were able to assemble was the drivetrain. Initially, this seemed to go smoothly, but upon driving some errors became very clear. We had forgotten to use Loctite and lock nuts on the wheel bolts, and a circlip was improperly installed. Therefore, the vibration caused a wheel to loosen enough to fly off! After the initial shocked gasps and joking accusations, we quickly set about remedying the problem.
Once test driving was possible once again, we realized two things; the stability wasn’t as good as we’d like, and the front of the drivetrain wouldn’t fit under the load-station. The first problem was remedied by removing the center-drop, as it wasn’t needed for easy turning any more thanks to the Omni-wheels at the back. The second was caused by the drivetrains front swapping from one end to the other because of the needs of other systems. Due to this, the raised gearboxes are too close to the load station when trying to get a hatch, this was solved by ‘padding’ the new front with some POM.
The laser cut parts came in after we had the drivetrain assembled. This gave us one very clear task. Filing. The edges of the metal were very sharp and not at all safe, so every laser-cut part needed its edges filed off. After many hours of this, all the parts were safe, and we could use them in assembly. The first system made with these new parts was the horizontal displacement. It also used some sliding tracks from the FIRST starter kit, pistons, and springs.
Following this, the welded parts for the lift were delivered. Two of the milled parts to attach the lift to the drivetrain were found to be slightly too big to fit into the beam. They needed to be shaved down with an angle grinder before being hammered into place. Care was taken to not attach the 3 level 1 parts at the top until we were sure they were straight. We also could not screw the lift supports into the drivetrain as holes had not been drilled for this.
When the full lift was assembled, the carrier suddenly got stuck in the bottom, at first the bearing blocks were suspected to be faulty, but then a rogue bolt was found in the U-beam, jamming the system. The bolt was easily removed, and the horizontal displacement was attached to the carrier.
With the lift assembled we were able to attach the climbing arms to it. Upon the first assembly, it was found that one arm lock worked, while the other didn’t. We knew that the arm wasn’t moving down far enough for the lock to hold it. However, we could not find any obvious differences that would cause this and chalked it up to a combination of the tolerances. To remedy this, we placed a plate under the locking mechanism of the offending arm to raise it. It was then found that the springs that pulled the arms upright were too strong, to the point they bent the lift beams when operating. These springs have been removed and weaker ones put in their place. The bend has since been fixed.
Unfortunately, due to late delivery, we have not yet been able to assemble the lifts gearbox. However, as soon as we get that delivery, we will be able to fully assemble the robot to begin testing and tweaking.